1. Field of the Invention
The present invention relates to a character display control circuit.
2. Description of the Related Art
There are times when various information such as current channel, time and volume is displayed at a given position on a television receiver. Such an information display is carried out by generating video signals for information display with an OSD (On Screen Display) circuit, controlled by a microcomputer, and by switching between analog video signals for television images and video signals for information display as appropriate. See, e.g., Japanese Patent Application Laid-Open Publication No. Hei. 10-108088.
FIG. 3 is a block diagram of a television receiver for describing a conventional OSD output.
The conventional television receiver comprises a microcomputer 500, a mixing circuit 600, a signal processing circuit 200 and a display 300.
The microcomputer 500 performs various information processing. The microcomputer 500 contains an OSD output circuit for OSD display of information, and the OSD output circuit outputs, to the mixing circuit 600, red, blue and green (herein after referred respectively to as R, G and B) data and data I (intensity) for adjusting RGB data levels.
The data I, intended to adjust the level between “0” and “1” of the RGB data, can be adjusted to, for example, an intermediate level.
The mixing circuit 600 adjusts the RGB data levels with the data I, thus outputting the result thereof.
The signal processing circuit 200 performs signal processing based on the output result of the mixing circuit 600, outputting signals R′, G′ and B′ obtained to the display 300.
As above, in conventional OSD display, the operation for adjusting R, G and B data levels, output by the microcomputer, according to the data I is handled by the externally attached mixing circuit 600. If the data I is not used, there are two possible display colors (“HIGH” (hereinafter H) and “LOW” (hereinafter L)) for each of R, G and B produced by the character display control circuit, resulting in 2×2×2=8 or eight possible combinations in total. That is, eight colors can be displayed, and the number of display colors can be further increased using the data I as shown in FIG. 3.
When the input data I is “L” (logic value of “0”), the mixing circuit 600 outputs data as is as normal R, G or B color. On the other hand, when the input data I is “H” (logic value of “1”), the mixing circuit 600 makes adjustment so that the color is lighter than normal—at an intermediate level, for example. In this case, there are, for example, 8+8−1=15 or 15 possible combinations of colors produced, making it possible to display 15 colors.
The reason for subtracting 1 in the above equation is that if RGB data are all “0” (black), the output is “0” despite adjustment of the display signal by the data I, causing the display color to remain unchanged.
Thus, the conventional OSD circuit adjusts the RGB data levels according to the data I using the mixing circuit 600 attached externally of the microcomputer 500, with up to 15 display colors available.
With the conventional OSD circuit, creation of colors other than the eight colors leads to the problem of increased scale as a result of use of an externally attached circuit for adjusting the RGB data and the data I. In the case of games and the like, on the other hand, the conventional 15 colors are short of meeting the demand for OSD display using more than 15 colors, for example.